The present invention relates to a method and apparatus for diagnosis of a combustion condition in an internal combustion engine and a control apparatus provided therewith.
An example of a conventional apparatus for combustion diagnosis is disclosed in JP-A-2-104978 (1990).
In accordance with the known apparatus for combustion diagnosis, judgement as to whether misfire is occurring or not is performed by detecting an electric current after a constant voltage is supplied to an ignition plug subsequent to sparking of the ignition plug. When the ignition plug sparks, the atmosphere around the ignition plug is ionized; and, accordingly, if a voltage is applied to the ignition plug, an electric current, that is an ionic current, flows between the contacts of the ignition plug. The ionic current is measured for a predetermined period as a sample, and the sample is compared with a predetermined current level for judging whether misfire is occurring or not. However, in accordance with the prior art, the diagnosis of the combustion condition is performed by comparison of an ionic current, which is measured at only one sampling time, with a predetermined current level, and, consequently, the prior art has a problem that judgement errors occur relatively frequently.